The present invention relates to transmissions in a communication network and in particular it is concerned with multiplexing and bundling techniques for transmission in a communication network.
Traditional networks are designed for TDM services (for instance SONET/SDH/PDH). These networks are typically designed for supporting peak usage of bandwidth requirements and require a high reliability. TDM systems must be designed with sufficient link margin to guarantee transmission even under worst case condition like rain and fading. Furthermore SONET/SDH radio systems typically install redundant links for radio protection switching. Thus under normal circumstances TDM networks are under utilized and have spare capacity. Besides the traditional transmission of TDM services there is an increasing demand for the transmission of computer data (e.g. Ethernet/IP). These data is “bursty” and is transmitted in packets. Packet networks profit from radio links which uses adaptive modulation to offer a higher bandwidth under good environmental conditions.
There is a demand for support of faster interface ports, too. Examples are Gigabit Ethernet for packet services or STM-4 for traditional TDM services. However, traditional TDM radio links are not designed for such high bandwidth. This is because of technical but also because of regulative reasons. Technical reasons comprise limited resolution of available ADCs (analog-digital-converters) and/or DAC (digital-analog-converters), complex design of highly selective analog wideband filters, desired system modularity (i.e. possibility to extend the capacity later), trade-offs between modulation order and oscillator phase noise sensibility, new technologies as digital amplifier linearization which requires much higher sampling rate than the bandwidth of the user data, thermal problems, etc. . . Regulative reasons comprise fixed assignment of maximum transmission power and channel bandwidth by regional regulation authorities.
Under the circumstances described above it is clear that it is often not possible to transmit higher data rates over a single radio link. Link bundling can be used to overcome this bottleneck. This allows the transmission of GbE or STM-4.
It is known in the art parallel usage of TDM and packet services. Adaptive modulation and coding is also known. However, the known techniques suffer from a limited bandwidth capacity limited to the capacity of the single therein described and suggested link.
Nowadays there exists radio system which bundles two or more synchronous radio channels to form an aggregated channel with a higher bandwidth (e.g. for transmission of a STM-4 channel over 2 or for 4 radio channels). These SDH or SONET radio transmission systems generally require a high reliability and use radio protection switching. However, the known mentioned implementation is not flexible and limited to very special cases, namely transmission of ST-4 over 2 or more radio links.
There are also many systems documented which aggregate multiple links to form a service independent port with a higher bandwidth as each single link. With a TDM sub layer like SDH high rate packet services are transmitted over an aggregation of virtual TDM links. ITU-T G.707 and ITU-T G.783 discloses such an inverse multiplexing technique for SDH networks (see VCAT). The Link Capacity Adjustment Scheme (LCAS) specified in ITU-T G.7042 allows dynamically changing the bandwidth of virtual concatenated containers. A more flexible system is described in Hari Adiseshu, Guru M. Parulkar and George Varghese: “A Reliable and Scalable Striping Protocol”, Proceedings SIGCOMM 1996, pp. 131-141. It is noted that these systems are initially designed for asynchronous links.
The mentioned prior art solutions suffer however from a series of problems and disadvantages as summarized above and in the following.
VCAT and LCAS described in ITU-T G.707/ITU-T G.783/ITU-T G.7042 are designed for SDH networks. These systems are not very effective (e.g. SDH overhead, resource requirements for handling of many VCG's members). Because of the SDH hierarchy these systems are designed for fixed link bandwidth which limits the use of adaptive modulation and coding.
The bundling systems described in the paper of Adiseshu et al. are designed for asynchronous links. With an asynchronous aggregation system it gets very complicated to handle adaptive modulation and coding. Although we may foresee solving this problem by packet transmission with sequence numbers, still such a solution would result in causing more latency. In particular the transmission of low rate TDM services in packets causes a high delay.
In summary, the prior art does not provide a resource efficient and flexible solution for aggregating data over a communication network. With reference to radio links, furthermore, there is no radio system which makes an effective use of resources.